Ionization in Low-Energy Atomic Collisions of Neon with Neon and Krypton with Krypton

Neutral atomic beams of neon and krypton have been used to measure the total-ionization cross section for symmetric collisions as a function of energy. The beams were produced by symmetric charge transfer of ions produced in an electron-impact ion source with low-energy electrons. Beam energies ranged from below the ionization thresholds to 2000 eV for neon and to 1000 eV for krypton. Neutral-beam intensities were determined by the measurement of slow- and scattered-ion currents generated in the charge-transfer cell. It is found that the Ne-Ne ionization cross section is a rather smoothly varying function of energy, while that for Kr-Kr collisions exhibits structure. The two cross sections become equal at approximately 130 eV incident energy, above which the Kr-Kr cross section remains below that for Ne-Ne. Results are compared with those by Flaks at higher energies, and those by Bussmann and Rostagni at intermediate energies.